Hydrofoil



D. Z. BAILEY Oct; 10, 1967 HYDROFOIL 4 Sheets-Sheet 2 Filed April 29. 1965 INVENTOR. DAV/D Z. BAILEY ATTORNEYS United States Patent Ofifice Patented Oct. 10, 1967 3,345,968 HYDROFOIL David Z. Bailey, Warwick, R1. (R9. Box 69, East Greenwich, RI. 02818) Filed Apr. 29, 1966, Ser. N0. 546,243 5 Claims. (Cl. 114-665) This invention rel-ates to hydrofoil craft and in particular to hydrofoil structure.

In recent years hydrofoil operation of waterborne craft has received considerable attention, at least in part because of the speed and economy of operation offered by this mode of transportation. Commercial hydrofoil construction, however, has generally been limited to ships of small displacement and to the use of the partially submerged V-foil having a fixed attack angle. In such a foil at any given speed lift is a function of the submerged depth of the foil and control of the attack angle during flight, except by changing the attitude of the craft, is not feasible. As a consequence, the flying height of the craft is a function of speed, and the range of useful flying speeds is limited for any given craft. The partially su' merged foil also suffers the disadvantage that the portions of the foil breaking the water surface, being designed to function as hydrofoils, are not properly designed to break the water surface and consequently exert drag and produce cavitation and ventilation undesirably.

These disadvantages of the partially submerged V-foil are avoided using a fully submerged, normally horizontal foil which is pivotallymounted on the lower end or ends of one or more vertical struts which are designed to break the surface of the water and, when submerged, to provide minimum drag. The fully submerged pivotally mounted hydrofoil has not seen significant commercial use, however, probably because the upward force components produced by the forward velocity of the craft with respect to the water necessary to raise the hull of the craft above the surface of the water during flying must be transmitted from the hydrofoil to the hull through one or more struts of hydrodynamic cross-section thereby producing high stress forces at points of juncture between component parts of the hydrofoil structure. The effect of such stresses upon pivot points between the strut or struts and the foil limits the load which can be transmitted from the foil to each strut. As the upward pressure of the water is exerted against the hydrofoil, the foil is also deformed producing a bending moment upon the hydrofoil which is highest at the point or points of connection of the foil with the strut or struts, tending to limit severely the permissible foil spread. When two or more struts are associated with a single foil the bending moment of the foil is transmitted through the struts to the points of juncture of the hydrofoil structure with the hull thereby exerting large stresses upon the connection joints between the struts and both the hull and the hydrofoil.

It is therefore an object of this invention to provide a fully submerged hydrofoil construction for surface watercraft in which the an le of attack can be varied during operation without the limitations imposed by the employment of one or more pivotal connections between the foil and its associated strut or struts.

It is a further object of this invention to provide a hydrofoil construction in which the effects of bending moments at the junctures of components of the foil and the rest of the foil structure are minimized and in which the transmission of bending moments to the juncture of the hydrofoil structure with the hull and superstructure are also minimized.

These and other objects of this invention are obtained utilizing a fully submerged hydrofoil construction in which a foil is rigidly attached to the lower end of a depending strut.

In one aspect of this invention the upper end of the strut is mounted to the bull or superstructure of the watercraft for oscillatory movement in a forward and aft plane about the hydrodynamic centerline of the foil or some other desired fixed transverse line as an axis. Such an arrangement thus provides the advantages of the pivotally mounted fully submerged foil without the limitations imposed by the pivot pin carrying the load. Since the load is transmitted through relatively rigid structure to the mount for the foil structure and since the portion of the mount for the foil structure which permits the oscillatory movement to simulate pivoting can be located above the waterline, the mount can be made sufiiciently heavy to take the load without the need to consider efficient hydrodynamic design for the mount. At the same time when the strut is oscillata'ble about the hydrodynamic centerline of the hydrofoil asan axis, changes in left produced by changes in attack angle caused by such oscillation do not result in a displacement of the location along the craft at which the lift is effectively applied to the craft. The same result is approximately achieved when the axis of oscillation of the shut is any fixed transverse line in the vicinity of the hydrodynamic centerline of the foil.

In another aspect of this invention the strut is provided with greater cross sections at its lower and upper ends than at its intermediate portion thereby to provide relatively large areas in cross section where it is affixed to the foil and to the mounting device by which it is attached to the hull or superstructure of the craft. Thus a bending moments transmitted by the foil, to the extent they produce stresses in the strut, tend to flex the strut at its relatively more narrow, but jointless intermediate portion, thus reducing the strain at the joints at both ends of the strut. Since the joints are located at portions of the strut having relatively greater cross section, they are better able to resist the stresses which are applied. By proper choice of cross-sectional variation in the strut, moreover, it is feasible to locate the narrow, intermediate portion of the strut at the desired flying waterline, thus reducing to a minimum the effects of water surface disturbance by the shut.

A better understanding of the practical application of the principles underlying this invention can be obtained from the appended drawings in which:

FIG. 1 is a front elevation of a simplified hydrofoil structure in accordance with this invention before loading stresses are exerted upon it;

FIG. 2 is the same view as FIG. 1 depicting the distortions produced upon loading;

FIG. 3 is an elevation of the starboard side of a watercraft employing hydrofoils in accordance with this invention;

FIG. 4 is a fragmentary front elevation of the hydrofoil structure of the watercraft shown in FIG. 3;

FIG. 5 is a sectional taken along line 55 of FIG. 4;

FIG. 6 is a starboard side view of the hydrofoil structure shown in FIGS. 3 and 4 including long and short period attack angle control devices;

FIG. 7 is a perspective view of a portion of the mounting device used to attach the hydrofoil structure to the Watercraft of FIGS. 3-6;

FIG. 8 is an interior elevation of the mounting device shown in FIG. 7; and

FIG. 9 is a simplified starboard side elevation of the hydrofoil structure shown in FIG. 3 etc., illustrating attack angle adjustment in accordance with this invention.

Referring more particularly to FIGS. 1 and 2, there is portrayed a simplified hydrofoil structure 10 including a horizontal load-bearing frame 11 supported upon a horizontal hydrofoil 12 by a pair of vertical main struts 13 and 14, the cross sections of which struts vary from greater dimensions at the ends to a smaller dimension preferably located approximately slightly below midway between the lower edge of load-bearing frame 11 and the upper edge of hydrofoil 12 and designated 15 and 16, respectively. Frame 11 is designed to be mounted beneath a watercraft to receive the weight of the craft during flying and is mounted to be oscillated in a forward and aft direction about the hydrodynamic centerline of foil 12 as an 'axis, as described more fully with reference to FIG. 3 etc. The joints between frame 11 and struts 13 and 14 and between foil 12 and structs 13 and 14 are all rigid. The length of hydrofoil 12 is soproportioned that struts 13 and 14 are mounted spaced along the length of hydrofoil 12 at spacings calculated to provide an even distribution of downward forces upon hydrofoil 12 when the weight of the craft is equally distributed along frame 11. When the external forces acting upon hydrofoil structure are minimal, struts 13 and 14 and hydrofoil 12 are normally vertical and horizontal, respectively, and the tensile stresses between the junctures of struts 13 and 14 with frame 11 and with hydrofoil 12, respectively, are negligible. However, upon loading of frame 11 during flying, the horizontal configuration of hydrofoil 12 is distorted, as depicted in exaggerated manner in FIG. 2. The uplift exerted by the sea upon hydrofoil 12 tends to apply a bending moment to the portion 17 of hydrofoil 12 lying between struts 13 and 14 while the remainder of hydrofoil 12 is subjected to a centilever action in response to the upward force of the water. The distortion produced within portion 17 of hydrofoil 12 pulls toward each other the lower ends of struts 13 and 14, thereby imparting a bending moment within struts 13 and 14 as Well as producing significant stresses at their junctures with both hydrofoil 12 and load frame 11. Maximum deflection of struts 13 and 14 under the applied bending moments are predetermined to take place at or near the points of minimum thickness 15 and 16 thereby reducing the strain produced at the points of juncture of struts 13 and 14 with frame 11 and with hydrofoil 12, and within most of structure 10.

Referring more particularly to FIG. 3, a surface Watercraft 20 is shown with a pair of main hydrofoil structures 21 and 21 and a rudder assembly 22. Hydrofoils 21 and 21 are disposed on the starboard and port sides of craft, respectively, in side-by-side relation with their hydrodynamic centerlines on a common axis extending transversely beneath craft 20 at a position calculated to lie beneath and somewhat forward of the barycenter of craft 211 when fully loaded and at its intended flying attitude. Foils 21 and 21' are completely symmetric with respect to a vertical plane centered on the forward aft centerline of craft 20, and all symmetrically corresponding parts have been given the same reference numerals, except that those parts in port hydrofoil structure 21 are distinguished from those in starboard hydrofoil structure 21 by the superscript Rudder assembly 22 is similar to the main support structure and includes an upper load frame 23 and a lower foil 24, both of which are secured to a pair of vertical rudder fins 25, with the load frame being mounted upon the lower end of a vertical shaft 26. The rotation of both shaft 26 and rudder is controlled by a steerage lever 27 which is mounted atop of and extends perpendicular to shaft 26. The upper section of shaft 26 remote from the foils passes slidably through the interior of a sleeve 28, the exterior of which is received by and secured pivotally to a clamp 29 connected to the piston of a hydraulic jack 30. The cylinder section of jack 30 is pivotally secured to the transom of craft 20 at an eye 31. Shaft 26 at a point below sleeve 28 passes through a loose fitting collar 32, mounted through the fantail 4 33 of craft 20 to which collar shaft 26 is pivotally connected by a pin 34.

Rudder fin 25 thus can be rotated about shaft 26 as an axis to control direction in a conventional manner. At the same time under the control of jack 30, shaft 26 can be oscillated in a forward and aft direction about pivot pin 34, to adjust the attitude of foil 24. Ordinarily foil 24 does not substantially contribute to supporting the weight of craft 20 and is adjustable in attitude solely for the purpose of controlling the attitude of craft 20. Note, however, that foil carries some weight in order to give the craft stability in the event of violent pitching. Load frame 23 is larger than foil 24 and is located between the rest and flying waterlines to give minimum drag during flying operation.

Referring also to FIGS. 4 and 6, it will be noted that starboard and port main hydrofoil structures 21 and 21' are locate-d along the central lower portion of watercraft 21). In View of the fact that hydrofoil structures 21 and 21' are identical except that they are symmetric, further description of them will be confined to starboard foil structure 21 which includes a hydrofoil 40 of hydrodynamic cross section having a horizontal hydrodynamic centerline 41 extending at right angles to the forward and aft line of craft 20. Hydrofoil structure 21 further includes a pair of struts 42a and 42]), the lower ends of which are fixedly connected to hydrofoil 40, and the upper ends of which struts are fixedly connected to a weight-bearing structure including long and short angularly displaced sidearrns, respectively, designated by reference numerals 43 and 44, and a vertical support arm 45.

Sidearms 43 and 44 are joined at one pair of ends at a rigid joint from which support arm 45 rises upwardly such that the assembly has the shape of an inverted Y. The remote ends of sidearms 43 and 44 are securely attached to the upper ends of struts 42a and 42]), respectively, and a brace 39 is connected between the upper ends of struts 42a and 42b to which it is securely aflixed at its ends, such that hydrofoil structure 21 effectively is a rigid structure.

A pair of bosses 46a and 46b mounted atop vertical support arm 45 provide connection terminals respectively through which the weight of craft 20 is in part placed on foil structure 21.

An elongated rigid rod 48, the upper end of which is supported by the superstructure of craft 20 is secured to hydrofoil support 21 at its lower end at eye 49 mounted atop horizontal sidearm 43 intermediate its ends. Rod 48, which can be employed to raise or lower the hydrofoil support dependent upon the mode of operation desired, provides a point at eye 49 on which the weight of craft 20 is in part placed on foil structure 21. While rod 48 is preferably adjustable in length to permit exact control of the position of hydrofoil 40 in relation to craft 20, a rod of fixed length can also be utilized.

As may be more clearly seen from FIG. 7, a pair of tubular, inverted U-shaped fittings 56a and 56b is rigidly secured in spaced relation to form a mounting device 47 by means of tubular horizontal braces 59 and 60. Frame 47 acts to transmit the weight of craft 20 to hydrofoil structure 21 through cams 66a and 66b which are secured to I-beams 50a .and 50b, respectively, mounted transversely of the hull of craft 20. There is also a protective shield 57 for an aperture in the hull through which a portion of frame 47 passes. The outboard ends of U-shaped fittings 56a and 56b taper to centrally apertured rectangular terminals which are bolted to bosses 46a and 46b on hydrofoil structure 21, while the inboard ends of U-shaped fittings 56a and 56b flair into tangential connection with tubular brace 59 to the ends of which they are affixed.

A beam 61, secured to the upper portions of fittings 56a and 56b by a pair of supports 58a and 58b, respectively, supports a pair of spaced plates 62a and 62b on its interior, shipboard side with the plates parallel and defining between them a horizontal slot extending in a fore and aft direction. A cylindrical roller 63 is mounted secured to I-beams 50a and 50b in craft for rotation about its axis in a vertical position in the slot between plates 62a and 62b. The diameter of cylinder 63 is less than the spacing of plates 62a and 62b, the function of cylinder 63 being to limit inboard and outboard movement of frame 47, but not to guide it.

The junction of the inner ends of fittings 56a and 56b with the ends of brace 59 are constructed as mounting points for a pair of cam followers 64a and 64b, respectively, and for a pair of rollers 65a and 65b, respectively, Cam followers 64a and 64b are mounted projecting outwardly of the inner ends of fittings 56a and 56b for rotation about horizontal axes extending transversely of craft 20, while rollers 65a and 65b are mounted above the position of cam followers 64a and 64b for rotation about axes in. a common fore and aft vertical plane which are canted oppositely such that such axes intersect on any desired transverse line located below the flying waterline of craft 20, preferably on the hydrodynamic centerline of foil 4%), as illustrate Cams66a and 66b in the form of wedge-shaped plates are mounted exteriorly of the hull on the ends of I-beams Stla and 50b, respectively, beneath an aperture in shield 57 through which fittings 56a and 56b pass in such a position that the undersurfaces of cams 66a and 66b bear against the upper sides of followers 64a and 64b, respectively, and such that rollers 65a and 65b, respectively, bear against the inner lower edges of cams 66a and 66b. The undersurfaces of cams 66a and 66b in contact with followers 64a and 6415 are oppositely inclined with the same angle of inclination and are perpendicular to planes including the hydrodynamic centerline 41 of foil 40 or to such other transverse line about which it is desired to cause foil 40 to oscillate in adjusting its attitude. A hydraulic jack 67 is secured between I-beam 50a and the junction of fitting 56b and brace 52 in such a manner that frame 47 can be moved in a fore and aft direction by jack 67. It will be apparent that foil structure 21 hangs as a dead weight when craft 20 has no forward motion with respect to the water. Under such circumstances followers 64a and 6412 fall free of cams 66a and 66b, and rollers 65a and 65b similarly move away (inwardly) from the cams. If such movement is not otherwise limited by the geometry of the device stops must be provided to perform such function. Plates 80a and 801) can thus be mounted beneath cams 66a and 66b to limit downward movement of followers 64a and 64b, and roller stops 81a and 8112 can be mounted on frame 47 to limit inward movement by contact with plates 82a and 82b, respectively, mounted inwardly of stops 81a and 81b.

Referring to FIG. 9, which shows in simplified manner the relationship between foil structure 21 and inclined cams 66a and 6612, it will be seen that the undersurfaces of cams 66a and 6611 are tangent to an are having as a center the intersection of the plane of the drawing with hydrodynamic centerl-ine 41 of foil 40. It will also be seen that for limited distances in the vicinity of cam followers 64a and 64b the unders'urfaces of plates 66a and 66b approximate such arc. As a consequence, as frame 47 is moved in a forward or aft direction, foil structure 21 oscillates about hydrodynamic centerline 41 as an axis. Rod 48 is pivotally connected to the superstructure of craft 20 to accommodate such movement of foil structure 21. Hydrofoil 40 can thus be changed in attitude with respect to craft 20 while no change occurs in the location along craft 20 in the point of application of the lift produced by forward movement of foil 40 through the water. The same result is approximately achieved when the interrelation of the geometrical configurations of the contacting surfaces of the cam followers and plates are dimensioned such that the axis of oscillation of struts 42a and 42b is any fixed transverse line in the vicinity of hydrodynamic centerline 41.

Side arms 43 and 44 are generally hollow and have cross sections terminating with a pointed leading edge 68 to provide a minimum of resistance to the forward motion of craft 20 at takeoff and from waves which may from time to time break over foil structure 21 during flight. The interiors of side arms 43 and 44 are preferably filled with a commercially manufactured buoyant foam 69, e.g. polyurethane, to reduce the effect of water seepage, and vertical braces are provided within horizontal side arms 43 and 44 to increase the load-bearing ability of each member.

Both the width and thickness of main struts 42a and 421), which are of hydrodynamic design to minimize drag, are tapered from greater cross sections at both ends of each to a smaller cross section designated 70a and 7%, respectively, intermediate the ends, and struts 42a and 4212 are solid bronz castings. Hydrofoil 40 is of uniform cross section and suitable hydrodynamic design to provide the required lift to support the weight of craft 20 at design speed with minimum drag. Foil 40 is preferably formed with a stainless steel skin supported on steel strength members with voids filled with rigid foam, such as polyurethane foam. It will be apparent that foil structure 21 functions in the manner described with reference to foil structure 10 described in FIGS. 1 and 2 to absorb bending moments in flexure of struts 42a and 42b to reduce the strain imposed on the joints between component parts of structure 21.

In operation, watercraft 20 is driven by a suitable propulsion arrangement, for example, by a power driven screw 71 located beneath fantail 33. After craft 20 has attained adequate speed without flying and with foils 40 and 40' at an attitude presenting a low or non-existent attack angle, lift for takeoff is developed by oscillating foil structures 21 and 21' counterclockwise, as seen in FIG. 3, to provide a positive attack angle. Rudder assembly 22 at the same time can be oscillated slightly by moving the upper end of shaft 26 forward to increase the attack angle of foils 40 and 40' by changing the attitude of craft 20 as well. As flying height is obtained, these procedures are reversed to level craft 20 off. Preferably at flying height screw 71 is about half-submerged, and the water surface breaks at narrow portions 70a and 70b of foil structure 21 and at the corresponding portions of foil structure 21'. It will be appreciated that flying height is thereafter maintained by adjusting rudder assembly 22 for proper fore and aft trim and by adjusting foil structures 21 and 21 together to maintain height and oppositely to adjust transverse trim.

Automatic control of the attitude of hydrofoils 40 and 40 is not only feasible but desirable. To this end in FIG. 6 there is illustrated a float 72 attached pivotally to the lower end of a rod 74 slidably received in the lower end of a sleeve 73 secured to craft 20 aft of foil structure 21 and 74. The extension of rod 74 in sleeve 73 indicates the position of float 72 and hence locates the Waterline in flight. A control mechanism of conventional nature corrects the attitude of foil 40 by means of jack 67 to reciprocate frame 47 in a forward and aft direction. The control mechanism should be damped to provide a slow, i.e., long period, correction to a desired flying height. Additionally a sensor foil 77, attached to a strut 76 at its lower end so as to follow a stream line path and thereby indicate the direction of movement of craft 20 in the water is suspended immediately in front of foil 40 to provide control the attitude of foil 40 to maintain a constant angle of attack in a short period control system such as described in Patent No. 2,773,467.

I claim:

1. In combination:

(a) a watercraft,

(b) a hydrofoil structure including (i) hydrofoil having a hydrodynamic centerline and (ii) strut means having said hydrofoil secured rigidly thereto, and

(c) mounting means on said watercraft supporting said strut means with said hydrofoil in a fully submerged position to provide a lifting component along said hydrodynamic centerline when said craft has forward velocity across the surface of a body of water, said mounting means including (i) means for oscillating said hydrofoil structure relative to said craft about a fixed transverse axis in the vicinity of said hydrodynamic centerline.

2. The combination according to claim 1 in which said means for oscillating said hydrofoil structure includes cam means having a cam surface approximating an arcuate surface centered on said transverse axis.

3. The combination according to claim 2 in which said cam means includes (a) a pair of inclined plates the undersurfaces of which define a pair of said cam surfaces and (b) a pair of cam followers riding against said undersurfaces, said plates being aflixed to said watercraft and said followers being mounted on said hydrofoil structure.

4. The combination according to claim 1 in which said strut means includes (a) a pair of struts, spaced apart and each rigidly secured at the lower end thereof to said hydrofoil, and in which said hydrofoil structure further includes (b) a load-bearing frame rigidly secured to the upper ends of said struts, each of said struts being of greater cross section at the ends thereof than at an intermediate portion thereof, and said mounting means being associated with said loadbearing frame to support said strut means as aforesaid.

5. A hydrofoil structure including: (a) a hydrofoil adapted to be fully submerged, (b) a pair of struts spaced apart and rigidly secured to said hydrofoil at the lower ends of said struts, (c) a load-bearing frame rigidly secured to the upper ends of said struts, and (d) mounting means associated with said load-bearing frame adapted to support said structure, each of said struts being of greater cross section at the ends thereof than at an intermediate portion thereof.

References Cited UNITED STATES PATENTS 2,709,979 6/1955 Bush et al. l14-66.5

3,031,999 5/1962 rBader 11466.5

MILTON BUCHLER, Primary Examiner.

A. H. FARRELL, Examiner. 

1. IN COMBINATION: (A) A WATERCRAFT, (B) A HYDROFOIL STRUCTURE INCLUDING (I) HYDROFOIL HAVING A HYDRODYNAMIC CENTERLINE AND (II) STRUT MEANS HAVING SAID HYDROFOIL SECURED RIGIDLY THERTO, AND (C) MOUNTING MEANS ON SAID WATERCRAFT SUPPORTING SAID STRUT MEANS WITH SAID HYDROFOIL IN A FULL SUBMERGED POSITION TO PROVIDE A LIFTING COMPONENT ALONG SAID HYDRODYNAMIC CENTERLINE WHEN SAID CRAFT HAS FORWARD VELOCITY ACROSS THE SURFACE OF A BODY OF WATER, SAID MOUNTING MEANS INCLUDING (I) MEANS FOR OSCILLATING SAID HYDROFOIL STRUCTURE RELATIVE TO SAID CRAFT ABOUT A FIXED TRANSVERSE AXIS IN THE VICINITY OF SAID HYDRODYNAMIC CENTERLINE. 